Devices and compositions for the continuous dewetting of surfaces are already known and were described, for example, in Patents FR 1,541,592, FR 2,229,308 and U.S. Pat. No. 4,182,687. The last particularly describes a dewetting composition consisting of a chlorofluorocarbon, principally 1,1,2-trichloro-1,2,2-trifluoroethane, containing a quaternary ammonium mono- or dialkyl phosphate as surface-active agent. This surface-active agent can be formed in situ by reaction of a mono- or dialkylphosphoric acid, a quaternary ammonium chloride and an alkylamine in the chlorofluorocarbon.
In a continuous drying process which involves the separation of the entrained water before the recycling of the dewetting composition, it is desirable that the emulsion formed by the dewetting composition with the extracted water rapidly should separate into two phases in order to allow the aqueous layer to be removed before the dewetting composition is recycled.
In order to improve the rate of deemulsification of dewetting compositions based on quaternary ammonium mono- or dialkyl phosphate, Patent FR 2,522,007 recommended the replacement of the alkylamine of U.S. Pat. No. 4,182,687 by a fluorinated amine of general formula: ##STR1## in which R.sub.F represents a linear or branched perfluoroalkyl radical containing from 2 to 20 carbon atoms, X denotes an optionally partially halogenated, divalently-bonded group, and the symbols R.sup.1 and R.sup.2, which are identical or different, each represent a hydrogen atom or an alkyl or hydroxyalkyl radical containing 1 to 4 carbon atoms.
The dewetting compositions of this French Patent are prepared by mixing, in the chlorofluorocarbon solvent, a mono- or dialkylphosphoric acid of general formula: EQU (RO).sub.p (HO).sub.2-p PO.sub.2 H (II)
in which p is a number ranging from 1 to 2 and R denotes a linear or branched alkyl radical containing from 1 to 18 carbon atoms, a quaternary ammonium chloride of general formula: EQU R'.sub.2 N.sup..sym. R".sub.2 Cl.sup..crclbar. (III)
in which R' denotes a linear or branched alkyl radical containing from 6 to 18 carbon atoms and R" is a methyl or ethyl radical, and a fluorinated amine of formula (I) above. This method of preparation leads to the formation of a precipitate of the hydrochloride of the fluorinated amine which it is desirable to remove by filtration to give a perfectly homogeneous dewetting composition.
It has now been found that the de-emulsification time can be considerably reduced further and the separation of the aqueous and organic phases thus accelerated by replacing a portion of the fluorinated amine by an alkaline base and by introducing the quaternary ammonium chloride of formula (III) last. This additionally allows a precipitation, even partial, of the hydrochloride of the fluorinated amine to be avoided.